Device for controlling the cooling flows of gas turbines

ABSTRACT

The inner barrel of a turbine has a plurality of holes for receiving compressor discharge air and flowing such air within the inner barrel. A plurality of replaceable nozzles having internal bores of different diameters are selectively screw threaded into the openings of the inner barrel body enabling, with different diameters, a variation in the flow of compressor discharge air entering the inner barrel.

This application is the US national phase of international applicationPCT/IB01/01297 filed May 15, 2001, which designated the US.

The present invention relates to a device for controlling the coolingflows of gas turbines.

As is known, gas turbines comprise a compressor, to which air is fedfrom the external environment so as to bring it up to pressure.

The air under pressure passes into a series of combustion chambers whichterminate in a nozzle and into each of which an injector feeds fuelwhich is mixed with the air so as to form a combustible air mixture tobe burned.

The turbine converts the enthalpy of the gases combusted in theaforementioned combustion chamber into mechanical energy available for auser.

The present invention refers, in particular, to the outlet zone of thegas turbine compressor.

By way of introduction of the technical problems solved by the presentinvention, it should be noted that the constant attempt to increase theefficiency of gas turbines is subject to the requirement foroptimisation of all the flows inside the turbine engines.

In particular, the air supplied from the compression stages, since ithas been produced with considerable expenditure in terms of thethermodynamic cycle, must be used as far as possible for combustion,instead of for cooling or confining functions which moreover arerequired in the most critical hot zones.

The problem which is posed in this context is therefore that of correctmetering of this air in the various zones, taking into account that theamount of air required is variable depending on the operatingconditions, the age and the degree of wear or soiling of the turbineengine, its components and the dimensional variations of the componentsduring the transients.

In fact, in the event of an insufficient air flow, the consequences are,at best, a significant reduction in the life of the components with thepossibility of blade failure and fires.

It is pointed out here, incidentally, that these factors may have anegative effect resulting in an increase in costs for users.

In order to understand more fully the technical problems involved in thepresent invention, reference should be made first of all to FIGS. 1 to3, which show, respectively: a cross-sectional view of a gas turbineaccording to the prior art, denoted overall by the reference number 20;an enlarged view of the outlet zone of the compressor 21 of the gasturbine 20; and the conventional solution for controlling the coolingflows of the gas turbine 20 which may envisage fixed bores 22 in thebody 50 of the inner barrel 23.

In greater detail, FIG. 1 shows a gas turbine 20 provided with acompressor 21 with which an inner barrel 23 and a load-bearing bolster24 are associated; FIG. 1 also shows, among other things, the rotors 25and 26 of the turbine 20.

Examining in greater detail FIG. 2, it is possible to see the casing 27and the blades 28, forming part of the compressor 21, the outletdiffuser 29 of the compressor 21, the venting outlet 33 of theload-bearing bolster 24 and the air seals 30 and 31 of the inner barrel23; FIG. 2 also shows a portion of the rotor 32.

The solutions currently used for correct metering of the air flowsintended for cooling and sealing consist in the specific definition oforifices on the supply tubes/ducts and determination of the degree ofplay between rotating members and labyrinths formed in complementarystator components.

Orifices and labyrinths (see FIG. 3) are therefore interdependent from adesign point of view and precisely determined during finalisation of theprototype, so that extreme situations and deviations in design can besafely handled.

This means that these adjustments and tolerances are therefore definedby the manufacturer during assembly.

However, the need for an increase in the efficiency of the machines onthe part of customers has resulted in a reduction in the air flows tothe absolute minimum necessary, with the application of seals which areincreasingly efficient—often excessively so—with the serious risksmentioned above.

In particular, there has been a tendency to reduce the amount of airwhich escapes from the compressor 21 towards the innermost portions ofthe machine 20 (FIGS. 1-2), in particular in the zone located inside theinner barrel 22.

This air, passing through a first barrier of labyrinth seals, thenescapes from the vent of the load-bearing bolster 24 of the compressor21 and through the front interspace of the first turbine rotor, throughthe labyrinth formed with the angel wings on the shanks of the bladesand the stationary seals mounted on the casing.

The function of this air is therefore that of providing a seal from theoil vapours in the bolster 24 and hot gases inside the turbine 20,cooling the turbine disk and removing the heat produced by means ofventilation friction inside the inner barrel 23.

Experience has shown that often, the compromise adopted between the needfor an increase in efficiency and reliability of the machine, sincethere is no possibility for adjustment, has resulted in a suddenreduction in reliability of the machine.

An object of the present invention is therefore to provide a device forcontrolling the cooling flows of gas turbines which is able to allow thepossibility of varying the air flow entering into the inner barrel,without the need for replacement of the latter.

More particularly, the invention aims to avoid any kind of disassemblyof the most important components of the turbine engine, while allowingvariation in the air flow into the inner barrel.

Another object of the invention is to provide a device for controllingthe cooling flows of the gas turbines which allows adjustment which iscustomized and repeatable over time, by simply stopping the machine andperforming simple operations involving the selection and replacement ofsuitable component parts.

A further final object of the invention is to provide a device forcontrolling the cooling flows of gas turbines which is advantageous froma cost point of view.

Last but not least, an object of the invention is to provide a devicefor controlling the cooling flows of gas turbines which is substantiallysafe and reliable.

These and other objects are achieved by a device for controlling thecooling flows of gas turbines, where the aforementioned gas turbine isprovided with a compressor with which an inner barrel and a load-bearingbolster are associated, characterized in that it envisages thearrangement of a plurality of replaceable nozzles which have an internalbore with different diameters and which can be mounted in suitable holesformed in the substantially cylindrical body of the aforementioned innerbarrel so as to allow a variation in the flow of air entering into theaforementioned inner barrel, by means of the selection and replacementof at least some of the aforementioned nozzles with other nozzles havingan internal bore with suitable diameters.

According to a preferred embodiment of the present invention, each ofthe aforementioned nozzles has a threaded section able to engage with acorresponding internally threaded section present in a hole formed inthe aforementioned inner barrel.

According to a further preferred embodiment of the present invention,each replaceable nozzle has a cylindrical section with a diametersmaller than that of the threaded section and a pair of incisions forengagement with a magnetic-head spanner.

According to another preferred-embodiment of the present invention, thenozzles are inserted by means of a guide tube and a magnetic-headspanner, the guide tube being inserted inside a corresponding holepresent in the casing of the aforementioned compressor.

More particularly, the guide tube has a threaded collar for allowingengagement thereof with a corresponding hole present in the casing ofthe compressor.

The guide tube is inserted into the hole of the compressor casing bysliding it until the aforementioned threaded collar thereof is screwedinto the corresponding threading of the compressor casing with its endinside the machine making contact with the aforementioned inner barrel,so as to form a retaining and guiding channel inside which the nozzlesto be screwed into the body of the inner barrel can be passed.

According to yet another preferred embodiment of the present invention,during operation of the aforementioned gas turbine, the holes in thecompressor casing are closed using bolts, or other similar closingdevices, inserted in position after removal of the guide tubes.

The present invention relates, moreover, to the fact that, in order tofix the nozzles in the operating position, it is further envisaged usinga dimpling punch, which is used by employing the guide tube as a guidefor the striking point.

Further characteristic features of the invention are defined in theclaims accompanying the present patent application.

The further objects and advantages of the present invention, as well asits structural and functional characteristics, will emerge clearly froman examination of the description which follows and its accompanyingdrawings, which are provided purely by way of a non-limiting example andin which:

FIG. 1 shows a cross-sectional view of a gas turbine according to theprior art;

FIG. 2 shows a cross-sectional view of an enlargement of the outlet zoneof the compressor of the gas turbine according to FIG. 1;

FIG. 3 shows the conventional solution for controlling the cooling flowsof gas turbines, which envisages fixed bores in the body of the innerbarrel;

FIG. 4 shows a partially sectioned view of a nozzle forming part of thedevice for controlling the cooling flows of the gas turbines, accordingto the present invention;

FIG. 5 shows a top plan view of the nozzle according to FIG. 4;

FIG. 6 shows a partially sectioned view of the device for controllingthe cooling flows of the gas turbines, according to the presentinvention, during a first assembly stage; and

FIG. 7 shows a partially sectioned view of the device for controllingthe cooling flows of gas turbines, according to the present invention,in the operationally assembled condition.

With particular reference firstly to FIGS. 6-7, the device forcontrolling the cooling flows of gas turbines, according to the presentinvention, is denoted overall by the reference number 10.

The device 10 comprises a plurality of replaceable nozzles 11 which canbe mounted in suitable holes 14 formed in the body 50 of the innerbarrel 23.

With reference to FIGS. 4-5, the nozzle 11 has a threaded section 12able to engage with a corresponding internally threaded section 13present in the hole 14.

The nozzle 11 also has a cylindrical section 16 with a diameter smallerthan the diameter of the threaded section 12 and the diameter of theinnermost smooth section 14, and a pair of incisions 15 for engagementwith a magnetic-head spanner.

The invention also envisages the use of a special tool formed by a guidetube 17 and by the magnetic-head spanner.

The use of a dimpling punch is also envisaged.

The guide tube 17 also has a threaded collar 18 allowing engagementthereof with a corresponding hole 19 present in the casing 27 of thecompressor 21.

The hole 19 therefore has an internally threaded section 40.

As regards that stated above, the machining operations which must becarried out on the gas turbine 20 consist in the boring and threading ofthe external casing 27 of the compressor 21 and the boring and threadingof the inner barrel 23.

Once the useful area necessary for a nominally correct value of air tobe admitted into the inner barrel 23 has been defined, this area isdivided up into a suitable number of nozzles 11 with cross-sections ofsuitable diameter, to be screwed onto the cylindrical body 50 of theinner barrel 23 radially inside suitable threaded bores 14.

Opposite these bores 14, a corresponding number of threaded radial boresare formed in the casing 27 of the compressor 21, having the function ofproviding access to the replaceable nozzles 11 from the outside.

During operation of the gas turbine 20, these holes 19 are closed bybolts 41 and other similar closing devices.

The replaceable nozzles 11 obviously have internal bores 51 of suitablediameter.

The replaceable nozzles 11 are in fact provided in the form of sets orkits, with various diameters of the internal bore 51, the average valueof which corresponds to the nominally optimum design diameter.

Once the gas turbine 20 has been started using this initially attempteddiameter, the diameter which is most appropriate on the basis of thereadings provided by the machine instrumentation is then chosen.

The special tool for mounting the replaceable is nozzles consists, asalready mentioned, of a guide tube 17 and an insertable spanner which isprovided with a special magnetic cross head.

The guide tube 17 has two ends provided with a flat cut perpendicular tothe axis and a threaded collar 18 at one end, with a threading similarto that of the holes 19 for access to the casing 27 of the compressor21.

From an operational point of view, the guide tube 17 is inserted intothe hole 19 of the casing 27 by sliding it until its threaded collar 18is screwed into the corresponding threading of the casing 27.

This operation brings the end inside the machine into contact with theinner barrel 23 so as to form a retaining and guide channel inside whichthe nozzles 11 to be screwed into the body 50 of the inner barrel 23 canbe passed.

Therefore, after insertion of the magnetic head spanner, the nozzles 11are removed and inserted.

Once the replacement operation has been completed, the replaceablenozzles 11 must be fixed by means of dimpling, using the tube of thespecial tool, i.e. the guide tube 17, as a guide for the striking point.

After this operation has been completed, the guide tube 17 is thenunscrewed and the screw plugs 41 are inserted in place of them, insidethe hole 19, by means of the internal thread 40.

The spanner has a magnetized head so as to be able to work easily withany angle of inclination.

The theoretical and experimental results have been so satisfactory as todemonstrate that the system may be used on gas turbines which are widelyused.

Therefore, the solution proposed has the aim of being able to vary theflow of air entering into the inner barrel 23, without the need forreplacement of the latter or in any case without the disassembly of anyimportant component of the turbine engine, but by means of simple accessto the replaceable nozzles 11 using a special tool, i.e. the guide tube17, via holes 19 which are normally closed.

This is such as to allow adjustment which is customised and repeatableover time by simply stopping the machines 20 and replacing theappropriate calibrated nozzles 11.

From the description given the characteristic features of the device forcontrolling the cooling flows of gas turbines forming the subject of thepresent invention clearly emerge, as do the advantages thereof.

The following final comments and observations are added here so as todefine the aforementioned advantages with greater precision and clarity.

As a result of the invention described it is possible to vary the flowof air entering into the inner barrel 23 by simply gaining access to theremovable nozzles 11 using a special tool, via holes 19, which arenormally closed.

This feature allows adjustment which is customised and repeatable overtime, by simply stopping the machines and performing replacement withthe appropriate calibrated nozzles.

It is obvious that numerous variations may be made to the device forcontrolling the cooling flows of gas turbines, according to the presentinvention, without thereby departing from the novel features of theinventive idea described.

Finally it is obvious that, in the practical embodiment of theinvention, the materials, forms and dimensions of the detailsillustrated may be of any kind, depending on requirements, and that theymay be replaced with others which are equivalent from a technical pointof view.

The scope of the invention is defined by the accompanying claims.

What is claimed is:
 1. A device for controlling the cooling flow of a gas turbine comprising: a compressor having an inner barrel including a cylindrical body and a plurality of openings through the cylindrical body of the inner barrel in communication with compressor discharge air and flowing compressor discharge air into the inner barrel; a plurality of replaceable nozzles having internal bores of different diameters relative to one another and mountable in said holes to enable a selective variation in the flow of compressor discharge air into the inner barrel in response to selection and replacement of one or more of said nozzles with one or more other nozzles respectively having internal bores of different diameter.
 2. A device according to claim 1 wherein each of said nozzles includes a threaded section for threaded engagement with a corresponding internally threaded section of a corresponding hole formed in the inner barrel body.
 3. A device according to claim 2 wherein each of said replaceable nozzles includes a cylindrical section having a diameter smaller than that of said externally threaded section of said nozzle.
 4. A device according to claim 2 wherein each of said replaceable nozzles has a pair of incisions for engagement with a magnetic head spanner.
 5. A device according to claim 1 including a guide tube and a magnetic head spanner, said compressor including an outer casing, said guide tube being receivable through a hole in said casing.
 6. A device according to claim 5 wherein said hole through said casing has female threads, said guide tube having a male threaded collar for threaded engagement with the female threaded hole of the casing.
 7. A device according to claim 6 wherein said guide tube is threaded into said hole of said casing and has a distal end for contact with the inner barrel body to form a retaining and guide channel, said nozzles being receivable through said channel for threaded engagement with the holes through the inner barrel body.
 8. A device according to claim 7 wherein said nozzles are staked to said inner barrel body by a dimpling punch received through said guide tube.
 9. A device according to claim 6 wherein during operation of the gas turbine, closure devices are mounted in said holes through said outer casing upon removal of said guide tube to close the outer casing holes. 